1. Field of the Invention
The present invention relates to a technique for correcting distortion of an image caused by tilt projection of a projection-type image display apparatus.
2. Discussion of the Background
FIGS. 18(A)-18(D) are explanatory diagrams showing an image projection by a conventional projection-type display apparatus. Generally, a projection-type display apparatus 20 modulates incident light from a light source by a light modulating unit such as a liquid crystal light valve (liquid crystal panel). The modulated light emitted from the liquid crystal light valve passes through a projecting optical system and is projected on a screen 30. That is, such a projection-type display apparatus enlarges and displays the image displayed on the liquid crystal light valve onto the screen 30.
As shown in FIG. 18(A), if the projection-type display apparatus 20 is positioned so the optical axis 20c of the projection-type display apparatus 20 matches a normal line 30n of the center position of the screen 30, the image 32 projected on the screen 30 is an undistorted image (hereinafter referred to as a xe2x80x9cnormal imagexe2x80x9d) similar to an image represented by image signals supplied to the liquid crystal light valve (FIG. 18(B)). However, such an arrangement is problematic if the projection-type display apparatus is situated between the user and the screen, since the projection-type display apparatus blocks the view of the user observing the projected image.
Now, a general arrangement is to position the projection-type display apparatus 20 at a position lower than that shown in FIG. 18(A) (a higher position will suffice as well) as shown in FIG. 18(C), so the angle xcex8p between an optical axis 20c of the projection-type display apparatus 20 and the normal line 30n of the screen 30 (this being hereinafter referred to as xe2x80x9ctilt anglexe2x80x9d) is more than 0 degrees. Image projection with a projection-type display apparatus positioned with such a certain tilt angle is generally referred to as xe2x80x9ctilt projection.xe2x80x9d However, if the projection-type display apparatus is situated so as to perform tilt projection, an image 34 projected on the screen 30 is enlarged in the vertical upwards direction more than an image 32, as shown in FIG. 18(D). In addition, a trapezoid-shaped distortion (also called xe2x80x9ckeystone distortionxe2x80x9d or xe2x80x9ctilt distortionxe2x80x9d), in which the image is enlarged horizontally at the upper edge, is generated. Hereinafter, the trapezoid-shaped image displayed on the screen will be referred to as a xe2x80x9cdistorted image.xe2x80x9d Incidentally, if the projection-type display apparatus is situated at a high position, a trapezoid-shaped distortion, in which the image is enlarged horizontally at the lower edge, is generated. The greater the tilt angle xcex8p, the more this trapezoid distortion increases.
Such trapezoid distortion can be optically corrected by electrically processing the image. FIGS. 19(A) and 19(B) are explanatory diagrams showing a method for electrically processing the image to correct the trapezoid distortion. In FIG. 19(A), a lower edge of an image 34 (distorted image) projected on the screen 30 for tilt projection, and that of an image 32 (normal image) projected on the screen 30 for no tilt projection are positioned at the bottom of the figure. To remove the distortion in the distorted image 34 and obtain an image 34xe2x80x2 similar to the normal image 32 (FIG. 19(B)), image signals should be provided to the liquid crystal light valve so the image projected on the screen 30 would be the corrected image 32xe2x80x2 shown by dotted lines in FIG. 19(B) if there is no tilt projection. That is, image signals representing the image portion 32xe2x80x2a, which is distorted in an opposite form as the distorted image 34, are to be applied to the liquid crystal light valve. Incidentally, hereinafter, the image portion 32xe2x80x2a will be referred to as an xe2x80x9ceffective image portion,xe2x80x9d and the other image portions 32xe2x80x2b (hatched) will be referred to as a xe2x80x9cnon-effective image portion.xe2x80x9d
The liquid crystal light valve has a plurality of pixels arrayed in a two-dimensional manner and pixel signals representing the image to be projected are input to each pixel, thus modulating the incident light. Accordingly, there is the need to provide pixel signals to all of the pixels in the liquid crystal light valve. To this end, of the corrected image 32xe2x80x2, pixel signals representing the image to be displayed are provided to the pixels of the liquid crystal light valve corresponding to the effective image portion 32xe2x80x2a. In addition, pixel signals representing black are provided to the non-effective image portion 32xe2x80x2b so as to obtain an area where nothing is displayed. For tilt projection, providing the pixel signals representing the corrected image 32xe2x80x2 to the liquid crystal light valve allows the image projected on the screen 30 to not be the distorted image 34, but the undistorted image (normal image) 34xe2x80x2 is approximately similar to the image 32.
An example of such a correction method is described in Japanese Unexamined Patent Publication No. 8-98119. According to this correction method, the effective image portion 32xe2x80x2a of the corrected image 32xe2x80x2 and the non-effective image portion 32xe2x80x2b thereof are obtained from the relationship between the position of an arbitrary pixel FPxe2x80x2 in the image 34xe2x80x2 projected on the screen 30 (FIG. 19(B)) and the position of a corresponding pixel FP (FIG. 19(B)) in the corrected image 32xe2x80x2, as a function of the tilt angle xcex8p. Incidentally, the relationship between the position of the arbitrary pixel FPxe2x80x2 in the image 34xe2x80x2 and the position of the corresponding pixel FP in the corrected image 32xe2x80x2 is shown with the following expressions:                     Yb        =                  Vn          ·                                    sin              [                                                π                  2                                +                                                      tan                                          -                      1                                                        (                                                            Vn                      -                                              Vm                        2                                                              L                                    )                                            ]                                      sin              ⁢                              xe2x80x83                            [                                                π                  2                                -                                  θ                  ⁢                                      xe2x80x83                                    ⁢                  p                                -                                                      tan                                          -                      1                                                        (                                                            Vn                      -                                              Vm                        2                                                              L                                    )                                            ]                                                          (1a)                                Xb        =                  hn          ·                                    L              +                                                Yb                  ·                  sin                                ⁢                                  xe2x80x83                                ⁢                θ                ⁢                                  xe2x80x83                                ⁢                p                                      L                                              (1b)            
The parameter Yb represents a distance in the vertical direction from the lower edge of the projected image 34xe2x80x2 to the position of the pixel FPxe2x80x2. The parameter Xb represents a distance in the horizontal direction from the left edge of the projected image 34xe2x80x2 to the position of the pixel FPxe2x80x2. The parameter Vn represents a distance in the vertical direction from the lower edge of the corrected image 32xe2x80x2 to the position of the pixel FP. The parameter hn represents a distance in the horizontal direction from the left edge of the corrected image 32xe2x80x2 to the position of the pixel FP. In addition, the parameter Vm represents a distance between the lower edge and upper edge of the effective image portion 32xe2x80x2b within the corrected image 32xe2x80x2. The parameter L represents a distance from the projection lens of the projection-type display apparatus 20 to the screen 30. The parameter xcex8p represents the tilt angle in the vertical direction (i.e., the angle in the vertical direction between the optical axis 20c of the projection-type display apparatus 20 and the normal line 30n of the screen 30).
From the above Expressions (1a) and (1b), a determination can be made regarding to which pixels of the liquid crystal light valve the pixel signals for each pixel in the image 34xe2x80x2 should be provided in the event of projecting an image 34xe2x80x2 free of trapezoid distortion on the screen 30 while performing vertical tilt projection.
The above background example illustrates an example in which the optical axis 20c of the projection-type display apparatus 20 and the normal line 30n of the screen 30 match within a horizontal plane, and the optical axis 20c of the projection-type display apparatus 20 and the normal line 30n of the screen 30 do not match within a vertical plane so there is a tilt angle xcex8p, (i.e., in the case in which horizontally symmetrical trapezoid distortion occurs). However, in reality, when the optical axis 20c of the projection-type display apparatus 20 and the normal line 30n of the screen 30 do not match within a vertical plane, there are cases in which the projection-type display apparatus 20 is also tilted horizontally to the screen 30. In such cases, the trapezoid distortion is non-symmetrical in the horizontal direction, and the technique according to the above background example cannot correct distortion well.
Also, the above Expressions (1a) and (1b) depend on the distance L between the projection-type display apparatus 20 (projection lens) and the screen 30, in addition to the vertical tilt angle xcex8p. However, the distance L is a parameter which varies according to the environment of use. To use the above Expressions (1a) and (1b), the distance L has to be obtained and set for each environment of use, so it is difficult in actual practice to use the Expressions (1a) and (1b) to suitably correct trapezoid distortion.
Accordingly, an object of the present invention is to provide a technique to readily correct image distortion due to the tilt projection of an image onto a screen.
To solve the above-noted and other problems, the present invention provides a first image processing device configured to process an image to be formed at an image forming section of a projection-type display apparatus, which projects and displays on a screen an image formed at the image forming section. The image processing device includes an image correction section that produces a distortion-corrected image obtained by correcting a shape of an original image and that supplies the distortion-corrected image to the image forming section, to correct distortion in the displayed image caused when an undistorted original image formed at the image forming section is subjected to tilt projection onto the screen.
The image correction section includes a first correction section which determines a display pixel range between a display start position and a display end position of the distortion corrected image on each horizontal line of the image forming section, based on horizontal correction parameters representing distortion-correction amounts at left- and right-sides of the distortion-corrected image, which determines a first relationship between each pixel within the display pixel range and each pixel in the original image based on a relationship between the number of pixels in the display pixel range and the number of pixels in one line in the original image, and which produces the distortion-corrected image from the original image according to the first relation.
According to the first image processing device of the present invention, image distortion in the horizontal direction can be easily corrected based on horizontal correction parameters representing the amount of correction on the left side and right side of the distortion corrected image. The image forming section is not limited to an image display such as a CRT, but includes a light modulating mechanism such as light valves and spatial light modulating devices. Liquid crystal panels are an example of a light valve. An example of spatial light modulating devices is a device utilizing reflection from mirror elements arrayed as pixels.
It is preferable the horizontal correction parameters include at least two parameters representing the distortion correction amounts at the left- and right-sides of the distortion-corrected image, and in which the distortion correction amounts at the left- and right-sides can be independently set.
The independent settings of the distortion correction amounts at the left- and right-sides of the distortion corrected image allows easy correction even when the image distortion is horizontally non-symmetrical.
Also, it is preferable the first correction section includes a pixel filter processor for performing interpolation filtering, based on the original image, to pixels within the display pixel range of the distortion-corrected image.
According to the above configuration, image deterioration due to the absence of skipped pixels can be relieved.
It is also preferable the image correction section further includes a second correction section which determines a display line range between a display start line and a display end line of the distortion corrected image on the image forming section, based on vertical correction parameters representing distortion-correction amounts in the vertical direction of the distortion-corrected image, which determines a second relationship between each line within the display line range and each line in the original image, and which produces the distortion-corrected image from the original image according to the second relationship.
According to this configuration, image distortion in the vertical direction can be easily corrected by appropriate settings of vertical correction parameters.
It is preferable the second relationship is determined based on a height of a substantially trapezoid-shaped effective image portion in the distortion-corrected image and a height of the original image, and in which the second relationship represents that the number of lines in the original image corresponding to a specific line in the effective image portion is greater as the specific line comes closer to the smaller base of the substantially trapezoid-shaped form, and that the number of lines in the original image corresponding to a specific line in the effective image portion decreases as the specific line comes closer to the larger base of the substantially trapezoid-shaped form. This allows the second relationship to be easily determined.
The second relationship can be determined by the following expression:                                                         MLAD              =                              xe2x80x83                            ⁢                                                1                  RSY                                ·                                  [                                                            {                                              LAD                        -                                                  (                                                      IMGY                            -                            KSSY                                                    )                                                                    }                                        +                                                                                                                                          xe2x80x83                            ⁢                                                                                          (                                              IMGY                        -                        KSSY                                            )                                        ·                    sin                                    ⁢                                      {                                                                  π                        2                                            ·                                                                        LAD                          -                                                      (                                                          IMGY                              -                              KSSY                                                        )                                                                                                    KSSY                          -                          1                                                                                      }                                                  ]                                                                        (        2        )            
where MLAD represents a line position in the original image, RSY represents a ratio of a height of the display image area to a height of the original image, LAD represents a line position in the display line range, IMGY represents a height of the original image, and KSSY represents a height of the substantially trapezoid-shaped effective image portion.
Also, it is preferable the second correction section includes a line filter processor for performing interpolation filter processing, based on the original image, to lines within the display line range of the distortion-corrected image.
Thus, image deterioration due to the absence of skipped lines can be relieved.
The second image processing device according to the present invention is an image processing device configured to process an image to be formed at an image forming section of a projection-type display apparatus, which projects and displays on a screen an image formed at the image forming section. The image processing device includes an image correction section that produces a distortion-corrected image which is obtained by correcting a shape of an original image and that supplies the distortion-corrected image to the image forming section, to correct distortion in the displayed image caused when an undistorted original image formed at the image forming section is subjected to tilt projection onto the screen. The image correction section includes a reducing section that reduces the original image to produce a reduced image, and a horizontal correction section that enlarges each horizontal line in the reduced image by an enlargement ratio of at least 1, which depends on horizontal correction parameters representing distortion correction amounts of left- and right-sides of the distortion-corrected image and on a position of each horizontal line, and that produces a distortion-corrected image for correcting the left- and right-side distortion.
According to the second image processing device, image distortion in the horizontal direction can be easily corrected based on horizontal correction parameters representing the amount of correction on the left- and right-sides of the distortion corrected image. Further, a distortion corrected image can be produced by enlarging the reduced image by a ratio of one or greater, so the resolution of the distortion corrected image in the horizontal direction can be made to be approximately constant.
A horizontal width of the reduced image may be equal to a minimum horizontal width of the substantially trapezoid-shaped effective image portion in the distortion-corrected image.
It is preferable the horizontal correction parameters include at least two parameters representing the distortion correction amounts at the left- and right-sides of the distortion-corrected image, and in which the distortion correction amounts at the left- and right-sides can be independently set.
The independent settings of the distortion correction amounts at the left- and right-sides of the distortion corrected image allows easy correction even when the image distortion is horizontally non-symmetrical.
Also, it is preferable the horizontal correction section includes a pixel filter processor for performing interpolation filter processing, based on the reduced image, to pixels within the display pixel range of the distortion-corrected image.
According to the above configuration, image deterioration due to the absence of skipped pixels can be relieved.
Also, it is preferable a height in the vertical direction of the reduced image is equal to or less than a height in the vertical direction of the substantially trapezoid-shaped effective image portion in the distortion-corrected image, and the image correction section further includes a vertical correction section which determines a display line range between a display start line and a display end line of the distortion-corrected image at the image forming section, based on vertical correction parameters representing distortion-correction amounts in the vertical direction of the distortion-corrected image, which determines a relationship between each line within the display line range and each line in the reduced image, and which enlarges the reduced image based on the relation to produce the distortion-corrected image.
According to this configuration, image distortion in the vertical direction can be easily corrected by appropriate settings of vertical correction parameters. Further, a distortion corrected image can be produced by enlarging the reduced image based on the relationship of each line within the display line range and each line of the reduced image, so the resolution of the distortion corrected image in the vertical direction can be made to be approximately constant.
The relationship may be determined to adjust a vertical enlargement ratio from the reduced image to the distortion-corrected image at each vertical direction position so the substantially trapezoid-shaped effective image portion in the distortion-corrected image is enlarged from the reduced image so as to compensate for vertical distortion in the displayed image caused when an undistorted original image formed at the image forming section is subjected to tilt projection onto the screen.
Particularly, it is preferable the relationship is determined based on a height of a substantially trapezoid-shaped effective image portion in the distortion-corrected image and a height of the reduced image, and in which the relationship represents that the substantial number of lines in the original image corresponding to a specific line in the effective image portion is greater as the specific line comes closer to the smaller base of the substantially trapezoid-shaped form, and that the substantial number of lines in the original image corresponding to a specific line in the effective image portion decreases as the specific line comes closer to the larger base of the substantially trapezoid-shaped form.
Such an arrangement allows easy determination of the relationship.
The above relation can be determined by the following expression:                                                         MLAD              =                              xe2x80x83                            ⁢                                                {                                      LAD                    -                                          (                                              IMGY                        -                        KSSY                                            )                                                        }                                -                                                                                                        xe2x80x83                            ⁢                                                (                                      KSSY                    -                    MEMY                                    )                                ·                                                                                                        xe2x80x83                            ⁢                              [                                  1                  -                                      sin                    ⁢                                          {                                                                        π                          2                                                ·                                                                              KSSY                            -                                                          (                                                              LAD                                -                                                                  (                                                                      IMGY                                    -                                    KSSY                                                                    )                                                                                            )                                                                                                            KSSY                            -                            1                                                                                              }                                                                      ]                                                                        (        3        )            
where MLAD represents a line position in the original image, LAD represents a line position in the display line range, IMGY represents a height of the original image, KSSY represents a height of the substantially trapezoid-shaped effective image portion, and MEMY represents a height of the reduced image.
A first image processing method according to the present invention is an image processing method of processing an image to be formed at an image forming section of a projection-type display apparatus, which projects and displays on a screen an image formed at the image forming section. The method includes an image correction step of producing a distortion-corrected image obtained by correcting a shape of an original image and supplying the distortion-corrected image to the image forming section, to correct distortion in the displayed image caused when an undistorted original image formed at the image forming section is subjected to tilt projection onto the screen. The image correction step includes a first correction step of determining a display pixel range between a display start position and a display end position of the distortion corrected image on each horizontal line of the image forming section, based on horizontal correction parameters representing distortion-correction amounts at left- and right-sides of the distortion-corrected image, determining a first relationship between each pixel within the display pixel range and each pixel in the original image based on a relationship between the number of pixels in the display pixel range and the number of pixels in one line in the original image, and producing the distortion-corrected image from the original image according to the first relation.
A second image processing method according to the present invention is an image processing method of processing an image to be formed at an image forming section of a projection-type display apparatus, which projects and displays on a screen an image formed at the image forming section. The method includes an image correction step of producing a distortion-corrected image obtained by correcting a shape of an original image and supplies the distortion-corrected image to the image forming section, to correct distortion in the displayed image caused when an undistorted original image formed at the image forming section is subjected to tilt projection onto the screen. The image correction step includes a reduction step of reducing the original image to produce a reduced image and a horizontal correction step of enlarging each horizontal line in the reduced image by an enlargement ratio of at least 1 which depends on horizontal correction parameters representing distortion correction amounts of left- and right-sides of the distortion-corrected image and on a position of each horizontal line, and producing a distortion-corrected image for correcting the left- and right-side distortion.
According to the first and second image processing methods of the present invention, operation and advantages similar to those of the above image processing device can be attained.